In the event there is a network failure which causes a service being provided on a first path through the network to go down, it is common to invoke a protection switching mechanism whereby the service is switched over to another path.
Various approaches exist, such as 1+1 protection, where data is sent over both a main path and a second path at all times. This provides low data loss, but requires approximately twice the network resources for each service.
Another approach is 1:1 protection, where a second path is configured, and in which low priority traffic may use the second path until it is required, at which point the low priority traffic is pre-empted. This provides low data loss. Its use of network resources depends upon the availability of low priority traffic. Also the pre-emption of the low priority traffic is an undesired aspect.
Yet another approach is to employ routing table updates, where a protocol like OSPF is used to update routing tables upon a failure. This provides good network utilization, but there is a large data loss as the routing tables across the network are updated.
Another solution involves reconnection, where a new path is calculated and set up after the failure occurs. Again, this provides good network utilization, but there is substantial data loss as the new path is calculated and set up.
It is common to perform BER measurement in SONET networks, see for example U.S. Pat. No. 5,764,651 which teaches the generation of signal degrade conditions when the BER becomes a certain value, and signal fail if the BER is even worse than that. However, the detection of these conditions has only been used to trigger the above discussed protection mechanisms. The signal degrade conditions are sent to a network management platform where a warning alarm might be raised.
In U.S. Pat. No. 6,141,532, a system of deciding whether to connect a call through a primary or backup transmission line is disclosed. The reference teaches analyzing the quality of a transmission line by looking at C/N and BER and sending this to a forecaster. The forecaster decides the likelihood that a failure is in the process of occurring within some predetermined time, such as the “mean call holding time”. If a failure is significantly likely, the call is connected through a backup transmission line, and otherwise, the call is connected through the primary transmission line. The reference does not deal with performing protection switching after a call is connected and is ongoing.
It is noted that it is common to employ FEC (forward error correction) to allow a certain number of errors to be corrected. Because of this, the raw BER can increase to a certain value with no impact on the error rate in the corrected bit stream, i.e. the corrected BER. However, once the BER reaches this certain value, sometimes referred to as the “coding correction cliff”, incorrect decoding results in a large increase in the corrected BER. The correction capabilities of FEC codes decrease by several orders of magnitude once the raw BER reaches this value.